The oil, gas and petrochemical industry desires to efficiently obtain hydrocarbons and process the hydrocarbons to produce desired products. Refining processes involve upgrading, converting or separating hydrocarbons (e.g., crude oil) into different streams, such as gases, light naphtha, heavy naphtha, kerosene, diesel, atmospheric gas oil, asphalt, petroleum coke and heavy hydrocarbons or fuel oil. Similarly, natural gas may be converted into industrial fuel gas, liquefied natural gas (LNG), ethane, propane, liquefied petroleum gas (LPG), and natural gas liquids (NGLs). The oil and gas processes are also often integrated with petrochemical systems to convert refinery streams into chemical products such as ethylene, propylene or polyolefins.
To convert hydrocarbon feeds into petrochemical or basic chemicals, chemical conversion processes may be utilized. These processes typically involve using thermal or catalytic reactors or furnaces to produce reactive hydrocarbon products, such as acetylene, ethylene or propylene in different proportions. As an example, steam cracking reactors are commonly utilized to convert the hydrocarbon feed into ethylene and acetylene, which may be further processed into various chemical products. The steam cracking reactors are utilized because they provide feed flexibility by being able to utilize gas (e.g., ethane) and liquid (e.g., naphtha) feeds.
Historically, the oil and gas refineries utilize the higher value distillates from the hydrocarbon feed, which are typically fungible fuels, such as mogas, natural gas and diesel. As a result, the petrochemical refineries utilize the remaining fractions, such as ethane, propane, naphtha and virgin gas oil, in their processes. However, few chemical conversion processes are able to directly employ natural gas or the lower value refinery feeds, such as aromatic gas oils or fuel oils. As such, there is a need for a process that can produce ethylene and acetylene from different feeds, such as advantaged feeds (e.g., natural gas and/or aromatic gas oils).
To process these feeds, high-severity conditions (e.g., more severe operating conditions, such as higher temperatures) are generally involved to produce products having a higher value than the feed. High-severity conditions enable methane cracking and aromatic ring cracking, which do not occur at appreciable rates at typical low-severity conditions (e.g., conventional steam cracking conditions). At high-severity conditions, the primary products of thermal chemical conversion processes are acetylene and ethylene along with hydrogen (H2) and coke, which may vary in proportion depending on the temperatures, pressures, residence times and feed type utilized in the conversion process. High-severity and low-severity conversion processes are typically based on different pyrolysis reactors, which may include pyrolysis alone or integrated with combustion chemistry. That is, the reactors may include pyrolysis chemistry (e.g., thermochemical decomposition of feed at elevated temperatures in the absence of oxygen) alone or in combination with combustion chemistry (i.e., exothermic chemical reactions between a fuel and an oxidant). These pyrolysis reactors can be divided into different types of high-severity, which include partial combustion, indirect combustion, arc process and thermal pyrolysis, for example. Each of these pyrolysis types differs in the means of generating and transferring the heat for the pyrolysis, which for simplicity are discussed below as techniques, which include the low-severity and high-severity.
The first technique is a partial combustion process or reactor. The partial combustion process burns part of the hydrocarbon feed to supply the heat to pyrolyse the remaining portion of the feed. The partial combustion reactor includes pyrolysis chemistry and combustion chemistry with both chemistries occurring at the same time and with the products of both chemistries being an integral part of the reactor product. An example of this process is German Patent No. 875198 and U.S. Pat. No. 7,208,647. Specifically, U.S. Pat. No. 7,208,647 describes a partial combustion process that utilizes partial oxidation to convert methane into ethylene. Due to the nature of this process, however, an air separation plant is typically required and combustion products (e.g., carbon monoxide (CO) and carbon dioxide (CO2)) are significant components of reactor effluent that have to be managed. Further, this type of approach appears to be unsuitable for polymer grade ethylene used in the production of polyethylene due to the levels of CO and CO2, which are both polyethylene catalyst poisons. As a result, the partial combustion process has certain limitations, such as the requirement to remove the high levels of combustion products and associated processing or additional processing equipment.
The second technique of pyrolysis reactor is the indirect combustion reactor. The indirect combustion process involves contacting combustion product with the feed to be cracked in the reactor. As such, this process involves pyrolysis and combustion chemistry, but typically the combustion chemistry may occur at a different time or location and the pyrolysis chemistry, while occurring in the presence of combustion products, proceeds in a largely non-oxidative environment, resulting in the products of the two chemistries being an integral part of the reactor product. In a process used by Hoechst (High Temperature Pyrolysis) in the 1960s, the thermal energy from a hot combustion product is used to crack a feed in direct contact. Examples of these types of reactors are described in G.B. Patent No. 834419 and German Patent No. 1270537. As another example, the Kureha/UCC process is similar, except that the primary purpose of this process is to make ethylene. In this process, which is described generally in U.S. Pat. No. 3,419,632, the hydrocarbon feed is a crude oil or a distillate having a boiling point less than (<) 1050° C. Further, U.S. Pat. No. 7,208,647 describes an indirect combustion process, which directly contacts the combustion gas with the feed to be cracked. Similar to the discussion for the partial oxidation process, this approach suffers from the same limitations of having to have an air separation plant and manage the combustion products This type of reactor and associated process also requires an expensive active quench step to stop the pyrolysis chemistry (e.g., water or oil).
The third technique of pyrolysis reactor is an arc reactor, which includes plasma arc reactors and electric arc reactors. This process typically involves only pyrolysis chemistry. Arc reactors are commercially limited and typically operated in a few small plants and described in U.S. Pat. No. 1,860,624. This process involving this type of reactor typically uses a water absorption process for recovery of acetylene, which was initially developed in the 1940s. The electric arc process utilizes electric power to heat a feed. As an example, U.S. Pat. No. 7,119,240 describes an electric arc reactor and process. The drawback of the arc process is the high cost of utilities, such as electricity, required to generate the “arc” or plasma. As a result, this process is limited to small units integrated with supplies of “cheap” electricity, such as a hydroelectric plants or nuclear facilities.
The fourth technique of pyrolysis reactors is a thermal pyrolysis reactor. Thermal pyrolysis reactors involve heating a solid material (e.g., by combustion) and using the heated solid material to crack the pyrolysis feed. In the thermal pyrolysis processes, the combustion products are typically maintained separate from the pyrolysis hydrocarbon products (e.g., via pyrolysis chemistry alone). This pyrolysis technique involves various different types of reactors, such as a regenerative reactor (e.g., as used in the Wulff process) and others. U.S. Pat. No. 7,119,240 describes an exemplary process for the conversion of natural gas into ethylene. In this process, natural gas is cracked in a furnace, actively quenched, and processed in a hydrogenation reactor to produce ethylene.
The “Wulff” reactor, as described in the IHS, SRI Consulting's Process Economics Program “Acetylene” Report Number 16 (1966) and 16A (1982) along with U.S. Pat. Nos. 2,319,679; 2,678,339; 2,692,819; 3,024,094, and 3,093,697, uses a reverse-flow pyrolysis reactor, which is typically operated at temperatures of <1400° C., to produce olefins and alkynes, such as acetylene. The pyrolysis feed is heated by refractories which have previously been heated by combustion reactions. The pyrolysis feed is cracked, and then cooled outside of the reactor. The relatively slow quenching is a characteristic of the Wulff process that leads to coke and soot formation from using inefficient indirect heat transfer (e.g., from checker brick). Coke formation in the reactor provides fuel during the combustion cycle and excess coke or soot may be alleviated by using a light feed, i.e., a hydrocarbon containing a high proportion of hydrogen. However, because the indirect heat transfer limits the rate of heat input in the Wulff process, certain pyrolysis feeds, such as methane, may not be economically processed, which limits the feed flexibility for this process. As a result, these reactors typically have limitations, such as poor heat transfer and greater soot generation resulting in poorer selectivity to desired products.
While the prior art describes using different pyrolysis reactors, these reactors described include various limitations, which reduce the efficiency of the process. Accordingly, it is desirable to provide a process that converts hydrocarbon feeds into olefins, such as ethylene, in an enhanced manner with high-severity reactors types being integrated together in an efficient manner.